SPI vs UART trade-offs in Embedded C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize SPI communication with the correct clock polarity.

Embedded C

SPI_InitTypeDef SPI_InitStruct = {0};
SPI_InitStruct.ClockPolarity = [1];
// Other initialization code

Drag options to blanks, or click blank then click option'

AUART_STOPBITS_1

BSPI_POLARITY_HIGH

CUART_PARITY_NONE

DSPI_POLARITY_LOW

Attempts:

3 left

💡 Hint

Common Mistakes

Using UART constants instead of SPI constants for clock polarity.

SPI clock polarity must be set using SPI_POLARITY_LOW or SPI_POLARITY_HIGH. UART options are incorrect here.

2fill in blank

medium

Complete the code to send a byte over UART.

Embedded C

HAL_UART_Transmit(&huart1, &[1], 1, 1000);

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Atx_byte

Bdata

Cspi_data

Dbuffer

Attempts:

3 left

💡 Hint

Common Mistakes

Using SPI variable names instead of UART data variable.

The variable 'tx_byte' is typically used to hold the byte to send over UART.

3fill in blank

hard

Fix the error in the SPI data reception code by completing the blank.

Embedded C

HAL_SPI_Receive(&hspi2, [1], 1, 1000);

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A&rx_buffer

Brx_buffer

C&tx_buffer

Dtx_buffer

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the buffer variable without '&' causing runtime errors.

The receive function requires a pointer to the buffer where data will be stored, so '&rx_buffer' is correct.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters SPI data bytes greater than 128.

Embedded C

filtered_data = {byte: [1] for byte in spi_data if byte [2] 128}

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Abyte * 2

Bbyte + 1

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operator or incorrect value expression.

The comprehension doubles bytes greater than 128. So the condition is '>' and the value is 'byte * 2'.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps UART characters to their ASCII codes if code is less than 100.

Embedded C

ascii_map = [1]: ord([2]) for [3] in uart_chars if ord(char) < 100

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Achar

Dcode

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

We map each character 'char' to its ASCII code using ord(char) for chars in uart_chars with code less than 100.

Practice

1. Which of the following is a key advantage of SPI over UART?

easy

A. Simpler hardware design

B. Uses fewer wires

C. Better for long-distance communication

D. Faster data transfer speed

Solution

1. Step 1: Understand SPI characteristics

   SPI is known for high-speed data transfer and supports multiple devices with separate select lines.

2. Step 2: Compare with UART features

   UART uses fewer wires and is simpler but slower than SPI.

3. Final Answer:

   Faster data transfer speed -> Option D

4. Quick Check:

   SPI speed > UART speed [OK]

Hint: SPI is fast and complex; UART is simple and slow [OK]

Common Mistakes:

• Confusing wire count advantage
• Mixing speed with simplicity
• Assuming UART is faster

2. Which of the following is the correct way to describe UART wiring?

easy

A. Uses four wires including separate clock line

B. Uses two wires: TX and RX

C. Uses three wires: MOSI, MISO, and SCLK

D. Uses one wire for data and clock combined

Solution

1. Step 1: Recall UART wiring basics

   UART typically uses two wires: one for transmitting (TX) and one for receiving (RX).

2. Step 2: Eliminate other options

   SPI uses MOSI, MISO, and SCLK (3 wires), and UART does not use a separate clock line.

3. Final Answer:

   Uses two wires: TX and RX -> Option B

4. Quick Check:

   UART wires = TX + RX [OK]

Hint: UART always uses TX and RX wires only [OK]

Common Mistakes:

• Confusing SPI wires with UART
• Thinking UART needs clock wire
• Assuming UART uses more than two wires

3. Given the following scenario: You need to communicate with three sensors quickly on the same bus. Which interface is best and why? Sensor1, Sensor2, Sensor3 connected to MCU

medium

A. SPI, because it supports multiple devices with separate select lines

B. SPI, because it uses fewer wires than UART

C. UART, because it is faster than SPI

D. UART, because it supports multiple devices easily

Solution

1. Step 1: Analyze device count and speed needs

   Communicating with multiple sensors quickly requires an interface that supports multiple devices and high speed.

2. Step 2: Match interface features

   SPI supports multiple devices using separate chip select lines and is faster than UART, which is simpler but slower and not ideal for multiple devices on one bus.

3. Final Answer:

   SPI, because it supports multiple devices with separate select lines -> Option A

4. Quick Check:

   Multiple devices + speed = SPI [OK]

Hint: Multiple devices + speed = SPI choice [OK]

Common Mistakes:

• Choosing UART for multiple devices
• Confusing speed advantage
• Ignoring chip select lines in SPI

4. Identify the error in this SPI communication setup code snippet:

spi_init();
spi_select_device(1);
spi_send_byte(0xA5);
spi_deselect_device(1);
spi_send_byte(0x5A);

medium

A. No error, code is correct

B. Missing UART initialization

C. Sending data after deselecting device causes error

D. spi_select_device should be called twice before sending data

Solution

1. Step 1: Review SPI device selection logic

   Data should be sent only when the device is selected; sending after deselecting is invalid.

2. Step 2: Check code sequence

   After deselecting device 1, sending another byte without selecting a device is an error.

3. Final Answer:

   Sending data after deselecting device causes error -> Option C

4. Quick Check:

   Send data only when device selected [OK]

Hint: Always select device before sending data [OK]

Common Mistakes:

• Ignoring device select/deselect order
• Confusing UART with SPI code
• Assuming multiple sends allowed without select

5. You want to design a communication system for a device that is 10 meters away and requires minimal wiring. Which interface should you choose and why?

hard

A. UART, because it uses fewer wires and works better over longer distances

B. SPI, because it is faster and supports multiple devices

C. SPI, because it uses fewer wires than UART

D. UART, because it supports multiple devices easily

Solution

1. Step 1: Consider distance and wiring needs

   For 10 meters distance, simpler wiring and signal integrity are important.

2. Step 2: Match interface to requirements

   UART uses fewer wires (TX, RX) and is better suited for longer distances than SPI, which requires more wires and is better for short distances.

3. Final Answer:

   UART, because it uses fewer wires and works better over longer distances -> Option A

4. Quick Check:

   Long distance + fewer wires = UART [OK]

Hint: Long distance + minimal wires = UART [OK]

Common Mistakes:

• Choosing SPI for long distance
• Confusing wire count
• Ignoring distance limits of SPI